Automatic adjustment method of tracer head

ABSTRACT

Manual zero adjustment of a tracer head and adjustment of differential amplifiers for the tracer head are eliminated by a step of storing the outputs of differential amplifier circuits as zero-point offset amounts while maintaining the tracer head in a non-contact state, a step of successively maintaining the tracer head in a first and a second state, and while doing so, storing first and second coordinates of the tracer head in the first and second contact states, together with first and second amounts of displacement compensated for by the zero-point offset amounts, a step of calculating and storing gains of the differential amplifier circuits on the basis of the first and second coordinates and the first and second amounts of displacement compensated for by the zero-point offset amounts, and a step of effecting tracing control through the use of the stored zero-point offset amounts and gains. These steps are carried out under control of a processor.

BACKGROUND OF THE INVENTION

The present invention relates to an automatic adjustment method of atracer head for use in a tracing control system.

Heretofore, initial adjustment of a tracer head for use in a tracingcontrol system has been made manually. That is, zero adjustment of thetracer head, held in a non-contact state or out of contact with thesurface of a model, is effected so that the output of each differentialamplifier circuit for amplifying the output of a differentialtransformer may be reduced to zero, after which the tracer head isdisplaced as predetermined and the gain of the differential amplifiercircuit is adjusted so that its output may take a predetermined value atthis time.

However, this conventional method has the defects of not only involvinglong-time, complex adjustment but also dispersion in the cuttingaccuracy since the results of adjustment vary according to differentoperators.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an automatic tracerhead adjustment method which involves no manual operations, and henceincreases the cutting speed and accuracy.

The present invention includes a step of storing the output of eachdifferential amplifier circuit as a zero-point offset amount whilemaintaining the tracer head in the non-contact state; a step ofmaintaining the tracer head in a first and a second contact state oneafter the other, and while doing so, storing first and secondcoordinates of the tracer head in the first and second contact statesone after the other, together with first and second amounts of detectioncompensated for by the zero-point offset amount; a step of calculatingand storing the gain of the differential amplifier circuit on the basisof the first and second coordinates and the first and second amounts ofdetection compensated for by the zero-point offset amount; and a step ofcalculating an amount of displacement from an amount of detectionobtained by A/D converting a signal available from the tracer headthrough the use of the stored zero-point offset amount and gain undercontrol of a processor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating the arrangement of a tracingcontrol system to which an embodiment of the present invention isapplied; and

FIGS. 2 and 3 are flowcharts explanatory of the embodiment of thepresent invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 illustrates in block form the arrangement of a tracing controlsystem to which an embodiment of the present invention is applied.Reference character TR indicates a tracer head, ST a stylus, CT acutter, MAC a tracing machine, MX, MY and MZ servo motors in the X-, Y-and Z-axis directions, respectively, PCX, PCY and PCZ position sensors,CNTX, CNTY and CNTZ reversible counters for counting feedback pulsesfrom respective position sensors to indicate the current position of thetracer head, D/AX, D/AY and D/AZ digital-to-analog converters forconverting drive signals for the servo motors from digital to analogform, AMPX, AMPY and AMPZ differential amplifier circuits fordifferentially amplifying displacement signals from differentialtransformers of the tracer head, MPX a multiplexer for selectivelyswitching the outputs of the differential amplifier circuits, A/D ananalog-to-digital converter for converting the output of the multiplexerfrom analog to digital form, CPU a processor, MEM a memory comprised ofa data memory part M1 and a control program part M2, I/O a datainput/output device, KB a keyboard and OPP an operator panel.

The operation of the embodiment of the present invention in FIG. 1 willbe described with reference to the flowcharts shown in FIGS. 2 and 3.

The CPU starts its operation at step 1, in which it reads theX-coordinate X of the tracer head at the start of operation from thereversible counter CNTX via a bus BUS and stores it as an X-coordinateXST at the start of operation in the data memory part M1 of the memoryMEM. Incidentally, it is the tracing machine MAC that is actually drivenby the servo motors and the tracer head stands still, but itscoordinates are represented as coordinates relative to the tracingmachine MAC.

Next, in step 2 the absolute value of displacement EX in the X-axisdirection at the start of operation is compared with a predeterminedvalue EXOC. Since the stylus ST mounted on the tip of the tracer head TRis not in contact with a block BL at the start of operation, thedisplacement EX at this time naturally ought to be zero, but thedisplacement EX read out by the CPU via the multiplexer MPX, the A/Dconverter A/D and the bus BUS does not become zero in general because ofinequality between secondary winding outputs DX1 and DX2 of thetransformer provided in the stylus which results from positionaldeviations of iron cores of the transformer, or because of imbalancepresent in the differential amplifier circuit AMPX. When thedisplacement EX at the start of operation (when the tracer head is inthe non-contact state) is larger than the predetermined value EXOC,since predetermined accuracy of linearity cannot be expected, theoperation ends at step 3 raising an alarm. On the other hand, when thedisplacement EX in the non-contact state is smaller than thepredetermined value EXOC, the operation proceeds to step 4 in which thedisplacement EX is stored as a zero-point offset amount EXO of thedifferential amplifier circuit AMPX in the data memory part M1.

In the next step 5 the stylus ST is fed at a velocity -VXFT in theX-axis direction (precisely speaking, the tracing machine MAC is fed ata velocity VXFT in the X-axis direction), and in the next step 6 a checkis made to determine if the difference between the amount of currentdisplacement EX and the aforementioned offset amount EXO has exceeded apredetermined amount of displacement EXTC. If not, the abovesaid feedand check are repeated until the abovementioned difference exceeds thepredetermined amount of displacement. When the stylus moves into contactwith the block BL and the difference between the amount of currentdisplacement EX and the offset amount EXO exceeds the predeterminedvalue EXTC, the feed rate VX is changed to zero in step 7, after whichit is checked in step 8 whether the movement of the stylus in the X-axisdirection has stopped or not. That is, in step 8 a check is made todetermine if the content ERRX of an error counter (not shown) forcounting the difference between command pulses and feedback pulses fromthe position sensor PCX has become smaller than a predetermined residualerror ESL, and if the result of this checking is affirmative, then itwill be decided that the stylus has come to a standstill.

When the stylus has thus been stopped at a first standstill point, thedifference between the amount of current displacement EX and the offsetamount EXO, that is, the amount of displacement of the stylus at thefirst standstill position compensated for by the offset amount (theamount of first detection) is stored as EXG1 in the data memory part M1,and in step 10 the X-coordinate X of the first standstill point isstored as XG1 in the data memory part.

Upon completion of this storage, the operation proceeds to steps 11 and12, in which the stylus is fed toward the block BL at a predeterminedvelocity -VXFL until the X-coordinate X of the stylus becomes equal toXG1-XD, that is, until the stylus moves further toward the block BL thanthe abovesaid XG1 by XD. When this condition is fulfilled, the movementof the stylus in the X-axis direction is stopped in steps 13 and 14.

When the stylus has thus been stopped at a second standstill point, theprocessing by the CPU proceeds to step 15 shown in FIG. 3, in which thedifference between the amount of second current displacement EX and theoffset amount EXO, that is, the amount of displacement of the stylus atthe second standstill point compensated for by the offset amount (theamount of second detection) is stored as EXG2 in the data memory partM1, and in step 16 the X-coordinate x of the second standstill point isstored as XG2 in the data memory part.

Upon completion of this storage, the process by the CPU proceeds to step17, in which is calculated the ratio of the difference between theX-coordinates of the first and second standstill points, (XG2-XG1), tothe difference between the amounts of displacement compensated for bythe offset amount, (EXG2-EXG1), and this value with an inverse sign isstored as a gain KX of the differential amplifier circuit AMPX in thedata memory part M1.

After the gain KX has been calculated and stored as described above, thestylus is moved toward the operation starting point at a predeterminedvelocity VXFT in step 18 and, after being returned to the starting pointin steps 19, 20 and 21, it is stopped there.

After the zero-point offset amount EXO and the gain KX of thedifferential amplifier circuit AMPX for detecting displacement of thestylus in the X-axis direction have thus been stored, zero-point offsetamounts EYO and EZO and gains KY and KZ of the differential amplifiercircuits AMPY and AMPZ for detecting displacement of the stylus in theY- and Z-axis directions are stored respectively in blocks 30 and 40 ofthe same contents as the above-described steps 1 to 21, completing theentire process of the CPU.

The zero-point offset amount and gain of the differential amplifiercircuit for detecting displacement in each axis, thus stored in the datamemory part M1, will be used for zero-point compensation of the amountof displacement in each axis and correction of the gain in thesubsequent tracing operation. That is, when starting the subsequenttracing control, the CPU compensates for and corrects output data of theunadjusted differential amplifier circuits AMPX, AMPY and AMPZ on thebasis of the zero-point offset amounts and gains stored in the datamemory part M1, thus calculating the amounts of displacement. Lettingthe zero-point offset amounts and the gains of the respectivedifferential amplifier circuits be represented by EXO, EYO, EZO and KX,KY, KZ, the following calculations are conducted for input data EXi, EYiand EZi converted from analog to digital form, thereby obtainingcorrected amounts of displacement EX, EY and EZ. EX=KX (EXi-EXO); EY=KY(EYi-EYO); EZ=KZ (EZi-EZO).

While in the above embodiment the zero-point offset amounts and thegains are stored for the three axes while feeding the stylus in thethree axes one after another, it is also possible to store thezero-point offset amounts and the gains simultaneously for the threeaxes while feeding the stylus in a direction including any of thethree-axis components.

Further, although in the above embodiment the first standstill point forproviding the first contact state is set as the coordinate positionwhere a predetermined amount of displacement is obtained, it is alsopossible to set the first standstill point by providing predeterminedcoordinates on the basis of the preknown position and shape of the blockBL.

Similarly, the second standstill point can also be set as a point wherethe amount of displacement is larger than that at the first standstillpoint by a predetermined amount, instead of setting the secondstandstill point at a predetermined distance from the first standstillpoint for providing the second contact state.

Moreover, the first and second contact states are obtained by the firstand second standstill points in the above, but it is also possible toobtain the first and second contact states through utilization of theposition of the stylus which is moving at a feed rate sufficiently lowerthan the data read rate and processing throughput of the processor.

As described above in detail, according to the present invention, a stepof storing the output of each differential amplifier circuit as azero-point offset amount while maintaining the tracer head in thenon-contact state, a step of successively maintaining the tracer head infirst and second contact states, and while doing so, storing first andsecond coordinates of the tracer head in the first and second contactstates, together with first and second amounts of displacementcompensated for by the zero-point offset amount, a step of calculatingand storing the gain of the differential amplifier circuit on the basisof the first and second coordinates and the first and second amounts ofdisplacement compensated for by the zero-point offset, and a step ofperforming tracing control using the stored zero-point offset and gain,are carried out under control of a processor without involving anymanual operation, thus providing the advantage of increasing the cuttingspeed and accuracy.

What is claimed is:
 1. An automatic tracer head adjustment method for atracing control system which is provided with a tracer head,differential transformers mounted in the tracer head, differentialamplifier circuits for amplifying the difference between secondarywinding outputs of the respective differential transformers to detectthe amount of displacement of the tracer head, an analog-to-digitalconverter for converting the detected displacement signal of the tracerhead from analog to digital form, coordinate detecting means fordetecting the coordinates of the tracer head, a processor for processingthe amount of displacement of the tracer head converted to a digitalquantity and the coordinates of the tracer head, a memory for storingthe processed output of the processor and means for D/A converting adigital quantity for control from the processor to control the feed ofthe tracer head, said method comprising:a step of storing the output ofeach differential amplifier circuit as a zero-point offset amount whilethe tracer head is in a non-contact state; a step of placing the tracerhead in a first contact state, and while doing so, storing a firstcoordinate of the tracer head and a first amount of detectioncompensated for by the zero-point offset amount; a step of placing thetracer head in a second contact state from the first contact state, andwhile doing so, storing a second coordinate of the tracer head and asecond amount of detection compensated for by the zero-point offset; astep of calculating and storing a gain of each differential amplifiercircuit on the basis of the first and second coordinates and the firstand second amounts of detection compensated for by the zero-point offsetamount; and a step of calculating the amount of displacement of thetracer head from an amount of detection obtained by A/D converting asignal from the tracer head through the use of each stored zero-pointoffset amount and each gain under control of the processor.
 2. Themethod of claim 1, wherein said first and second contact states aredetermined by comparing first and second detection thresholds of saiddetection to a measured amount of detection compensated for by thezero-point offset amount.
 3. The method of claim 1, wherein said firstand second contact states are determined by comparing the coordinates ofthe tracer head to first and second coordinate thresholds.
 4. The methodof claim 1, wherein said second contact state is determined based on apredetermined value above said first amount of detection compensated forby the zero-point offset with respect to that of said first contactstate.
 5. The method of claim 1, said tracer control system having threeaxes, said method comprising storing a zero-point offset amount and again for each of said three axes simultaneously while feeding saidtracer head in a direction having components along each of said axes. 6.The method of claim 1, said system including a block having apredetermined position and shape which said tracer head can contact,said method comprising determining said first contact state on the basisof said predetermined position and shape of said block.
 7. The method ofclaim 1, wherein said tracer head is maintained in each of saidnon-contact and first and second contact states during the storing ofthe respective zero-point offset amount and first and second coordinatesand amounts of detection.
 8. An automatic tracer head adjustmentapparatus for a tracing control system, comprising:a tracer head;differential transformers mounted in said tracer head; differentialamplifier circuits, connected to said differential transformers, foramplifying the difference between secondary winding outputs of therespective differential transformers to detect the amount ofdisplacement of said tracer head and produce a detected displacementsignal; an analog-to-digital converter, connected to said differentialamplifier circuits, for converting the detected displacement signal ofthe tracer head from analog to digital form; coordinate detecting means,coupled to said tracer head, for detecting the coordinates of saidtracer head; a memory for storing a processed output; means for D/Aconverting a digital quantity for controlling the feed of the tracerhead; and processing means, connected to said analog-to-digitalconverter, said coordinate detecting means, said means for D/Aconverting and said memory, for storing the output of each differentialamplifier circuit from said analog-to-digital converter as a zero-pointoffset amount while the tracer head is in a non-contact state, placingthe tracer head in a first contact state, and while doing so, storing afirst coordinate of the tracer head and a first amount of detectioncompensated for by the zero-point offset amount, placing the tracer headin a second contact state from the first contact state, and while doingso, storing a second coordinate of the tracer head and a second amountof detection compensated for by the zero-point offset, calculating andstoring a gain of each differential amplifier circuit on the basis offirst and second coordinates and the first and second amounts ofdetection compensated for by the zero-point offset amount, andcalculating the amount of displacement of the tracer head from an amountof detection obtained by A/D converting a signal from the tracer headthrough the use of each stored zero-point offset amount and each gainunder control of the processor.
 9. An apparatus as recited in claim 8,wherein said tracer control system has three axes and said processingmeans stores a zero offset and a gain for each of said axes whilesimultaneously controlling the feeding of said tracer head in adirection having components along each of the axes.